Beta cell mass (BCM) and the functional state of islets are critical measures in assessing the magnitude of autoimmune destruction in type 1 diabetes (T1D). Progressive loss of BCM is also responsible for the secondary failure of clinical drugs in type 2 diabetes. Serum tests such as insulin/C-peptide do not reliably measure BCM, and currently the only accepted gold standard of measurement is autopsy. Targeting receptors located on beta cells, such as the glucagon like peptide-1 receptor (GLP-1R), could prove useful as a diagnostic, preventative, and clinical tool in assessing beta cell mass. Thus, there exists a need for imaging probes that can be used to: a) better understand the history of the islet and the pathophysiology of diabetes, b) enable earlier diagnosis of T1D, c) allow monitoring of therapeutic efficacy and durability of drugs, d) reveal image-able biomarkers useful in the discovery of new therapies, e) monitor islet transplantation, and e) be used to localize beta cell derived malignancies. The compositions and methods described herein address these and other needs.